System and method for providing color light sources in proximity to predetermined wavelength conversion structures

ABSTRACT

An optical device includes a light source with at least two radiation sources, and at least two layers of wavelength-modifying materials excited by the radiation sources that emit radiation in at least two predetermined wavelengths. Embodiments include a first plurality of n radiation sources configured to emit radiation at a first wavelength. The first plurality of radiation sources are in proximity to a second plurality of m of radiation sources configured to emit radiation at a second wavelength, the second wavelength being shorter than the first wavelength. The ratio between m and n is predetermined. The disclosed optical device also comprises at least two wavelength converting layers such that a first wavelength converting layer is configured to absorb a portion of radiation emitted by the second radiation sources, and a second wavelength converting layer configured to absorb a portion of radiation emitted by the second radiation sources.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 13/328,978, filed on Dec. 16, 2011, now allowed, which claims benefit under 35 USC §119(e) to U.S. Provisional Application No. 61/424,562, filed Dec. 17, 2010; which is a continuation-in-part to U.S. application Ser. No. 13/019,897, filed Feb. 2, 2011, which claims benefit under 35 USC §119(e) to U.S. Provisional Application No. 61/301,193, filed Feb. 3, 2010; which is a continuation-in-part to U.S. application Ser. No. 13/014,622, filed Jan. 26, 2011, which claims benefit under 35 USC §119(e) to U.S. Provisional Application No. 61/357,849, filed Jun. 23, 2010, each of which is incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The present disclosure relates generally to light emitting devices and, more particularly, to techniques for using wavelength conversion materials with light emitting devices.

The present disclosure is directed to optical devices. The disclosure provides a light source that includes two or more layers of phosphor materials excited by radiation sources that emit radiations in two or more wavelengths, with at least one of the radiation wavelength less than 440 nm. In a specific embodiment where LED radiation sources are used, LED radiation sources that emit ultra-violet (UV), violet (V), or near-ultraviolet (NUV) radiation are used to excite blue phosphor material. In various embodiments, red and green phosphor materials are used and the LED radiation sources are arranged in a specific pattern. In other embodiments red, green, and blue phosphor materials are used.

In the late 1800's, Thomas Edison invented the light bulb. The conventional light bulb, commonly called the “Edison bulb”, has been used for over one hundred years. The conventional light bulb uses a tungsten filament enclosed in a glass bulb sealed in a base, which is screwed into a socket. The socket is coupled to an AC power or DC power source. The conventional light bulb can be found commonly in houses, buildings, and outdoor lightings, and other areas requiring light. Unfortunately, drawbacks exist with the conventional Edison light bulb. That is, the conventional light bulb dissipates much thermal energy. More than 90% of the energy used for the conventional light bulb dissipates as thermal energy. Additionally, the conventional light bulb eventually fails due to evaporation of the tungsten filament.

Fluorescent lighting overcomes some of the drawbacks of the conventional light bulb. Fluorescent lighting uses an optically clear tube structure filled with a noble gas, and typically also contains mercury. A pair of electrodes is coupled between the gas and to an alternating power source through ballast to excite the mercury. Once the mercury has been excited, it discharges, emitting UV light. Typically, the optically clear tube is coated with phosphors, which are excited by the UV light to provide white light. Many building structures use fluorescent lighting and, more recently, fluorescent lighting has been fitted onto a base structure, which couples into a standard socket.

Solid state lighting techniques are also known. Solid state lighting relies upon semiconductor materials to produce light emitting diodes (LEDs). At first, red LEDs were used. Modern red LEDs use Aluminum Indium Gallium Phosphide (AlInGaP) semiconductor materials. Most recently, Shuji Nakamura pioneered the use of InGaN materials to produce LEDs emitting light in the blue color range for LEDs. The blue light LEDs led to innovations such as solid state white lighting, the blue laser diode, the Blu-Ray™ DVD player, and other developments. Blue-, violet-, or ultraviolet-emitting devices based on InGaN are used in conjunction with phosphors to provide white LEDs. Other colored LEDs have also been proposed.

One way of improving solid state light efficiency has been to use phosphor converted LEDs (pcLED) technology, where an LED emits radiation that excites phosphors, which in turn emit light. Unfortunately, conventional pcLEDs have been inadequate, especially for white light for general illumination applications. In particular, blue-excited pcLED configurations have the challenge that blue light leakage must be managed to provide a stable white output. This is difficult because blue light leakage depends on the peak emission wavelength which shifts with drive current and operating temperature. V- or NUV-excited pcLEDs avoid this problem, but have performance disadvantages due to increased Stokes' loss, as well as cascading conversion loss, since much of the V or NUV light pumps blue phosphor, which then excites green and red phosphors, rather than direct excitation of the green and red phosphors.

Therefore, it is desirable to have improved techniques for phosphor-based LED devices.

BRIEF SUMMARY OF THE INVENTION

The present disclosure is directed to optical devices. The disclosure provides a light source that includes two or more layers of phosphor materials excited by radiation sources that emit radiations in two or more wavelengths, with at least one of the radiation wavelengths less than 440 nm. In a specific embodiment where LED radiation sources are used, LED radiation sources that emit ultra-violet (UV), violet (V), or near-ultraviolet (NUV) radiation are used to excite blue phosphor material. In various embodiments, red and green phosphor materials are used and the LED radiation sources are arranged in a specific pattern. In other embodiments red, green, and blue phosphor materials are used.

In one embodiment, an optical device includes a submount having a surface. The device includes a first plurality n of radiation sources positioned on the surface configured to emit radiation characterized by a first wavelength with a range between about 380 nm to 470 nm. The device also includes a second plurality m of radiation sources positioned on the surface configured to emit radiation characterized by a second wavelength shorter than the first wavelength. The ratio between m and n is based on a selected wavelength. The device further includes a first wavelength converting layer configured to absorb at least a portion of radiation emitted by the first plurality of radiation sources and the second plurality of radiation sources. The first wavelength converting layer is associated with a wavelength emission ranging from 590 nm to 650 nm. The device includes a second wavelength converting layer configured to absorb at least a portion of radiation emitted by the first plurality of radiation sources and the second plurality of radiation sources. The second wavelength converting layer is associated with a wavelength emission ranging from 490 mn to 590 nm. The device additionally includes a third wavelength converting layer configured to absorb at least a portion of radiation emitted by the second plurality of radiation sources. The third wavelength converting layer is associated with a wavelength emission ranging from about 440 nm to about 490 nm.

In another embodiment, an optical device includes a submount having a surface. The device also includes a first plurality n of radiation sources configured to emit radiation characterized by a first wavelength with a range between about 380 nm to 470 nm. The device also includes a second plurality m of radiation sources configured to emit radiation characterized by a second wavelength shorter than the first wavelength. The second plurality of radiation sources are positioned on the surface and arranged in a specific pattern. The ratio between m and n is based on a selected wavelength. The device also includes a first wavelength converting layer associated with a wavelength emission ranging from 590 nm to 650 nm configured to absorb at least a portion of radiation emitted by the first plurality of radiation sources and the second plurality of radiation sources. The device further includes a second wavelength converting layer associated with a wavelength emission ranging from 490 mn to 590 nm configured to absorb at least a portion of radiation emitted by the first plurality of radiation sources and the second plurality of radiation sources. The device also includes a phosphor pattern associated with a wavelength emission ranging from 440 nm to 490 nm overlaying the second plurality of radiation sources configured to absorb at least a portion of radiation emitted by the second plurality of radiation sources. A further understanding of the nature and advantages of the present disclosure may be realized by reference to the latter portions of the specification and attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a simplified diagram illustrating a chip-array-based pcLED apparatus with an RGB phosphor mix for generating white light, according to an embodiment of the disclosure.

FIG. 1B is a simplified diagram illustrating construction of a radiation source comprised of light emitting diodes, according to some embodiments.

FIG. 1C is a simplified diagram illustrating an optical device embodied as a light source constructed using an array of LEDs juxtaposed with a cover member, according to some embodiments.

FIG. 1D is a simplified diagram illustrating an LED lamp having a base to provide a mount point for a light source, according to some embodiments.

FIG. 2 is a simplified diagram illustrating a chip-array-based apparatus 200 having green and red wavelength converting material, according to some embodiments.

FIG. 3A is a simplified diagram illustrating a conversion process, according to some embodiments.

FIG. 3B is a simplified diagram illustrating a conversion process, according to some embodiments.

FIG. 4 is a graph illustrating a light process chart by phosphor material, according to some embodiments.

FIG. 5 is a simplified diagram illustrating an optical device according to an embodiment of the present disclosure.

FIG. 6 is a simplified diagram illustrating an optical device according to an embodiment of the present disclosure.

FIG. 7 is a simplified graph illustrating performance of various embodiments of optical devices, according to embodiments of the present disclosure.

FIG. 8 is a simplified diagram illustrating an optical device having violet and blue LEDs according to an embodiment of the present disclosure.

FIG. 9 is a simplified diagram illustrating an optical device having violet and patterned blue LEDs according to an embodiment of the present disclosure.

FIG. 10 is a simplified diagram illustrating an optical device having violet and red LEDs according to an embodiment of the present disclosure.

FIG. 11 is a simplified diagram illustrating an optical device having violet and red LEDs according to an embodiment of the present disclosure.

FIG. 12A is a simplified diagram illustrating an optical device having red, green, and blue LEDs disposed within recesses, according to an embodiment of the present disclosure.

FIG. 12B is a simplified diagram illustrating an optical device having red, green, and blue LEDs disposed between barriers, according to an embodiment of the present disclosure.

FIG. 13 is an exploded view of an LED lamp, according to some embodiments.

FIG. 14 is an illustration of an LED system comprising an LED lamp, according to an embodiment of the present disclosure.

FIG. 15 is a block diagram of a system to perform certain operations to fabricate an optical device, according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Various types of phosphor-converted (pc) light-emitting diodes (LEDs) have been proposed in the past. Conventional pcLEDs include a blue LED with a yellow phosphor. UV or V-based phosphor-converted (pc) LEDs exhibit certain advantages in performance (compared to blue-pumped pcLEDs) such as high color rendering (broadband spectrum comprising phosphor emission) and accurate color control (e.g., as the violet “pump” light contributes little to the chromaticity).

FIG. 1A is a simplified diagram illustrating a chip-array-based pcLED apparatus with an RGB phosphor mix for generating white light. As shown in FIG. 1A, the pcLED apparatus 100 includes three layers of phosphor materials: blue phosphor material 104, red phosphor material 103, and green phosphor material 102. The phosphor materials are excited by radiations emitted by LED devices (e.g., LED device 101). As an example, the LED devices are each nominally monochromatic and emit in a similar wavelength range.

FIG. 1B is a simplified diagram illustrating construction of a radiation source comprised of light emitting diodes. As shown, the radiation source 120 constructed on a submount 111 upon which submount is a layer of sapphire or other insulator 112, upon which, further, are disposed one or more conductive contacts (e.g., conductive contact 114 ₁, conductive contact 114 ₂), arranged in an array where each conductive contact is spatially separated from any other conductive contact by an isolation gap 116. FIG. 1B shows two conductive contacts in a linear array, however other arrays are possible, and are described herein. Atop the conductive contacts are LED devices (e.g., LED device 115 ₁, LED device 115 ₂, LED device 115 _(N), etc.). The LED device is but one possibility for a radiation source, and other radiation sources are possible and envisioned, for example a radiation source can be a laser device.

In a specific embodiment, the devices and packages disclosed herein include at least one non-polar or at least one semi-polar radiation source (e.g. an LED or laser) disposed on a submount. The starting materials can comprise polar gallium nitride containing materials.

The radiation source 120 is not to be construed as conforming to a specific drawing scale, and in particular, many structural details are not included in FIG. 1B so as not to obscure understanding of the embodiments. In particular, the dimensions of the isolation gap of FIG. 1B serves to separate the conductive contacts (e.g., conductive contact 114 ₁, conductive contact 114 ₂) one from another, and in some embodiments, the isolation is relatively wider, or deeper, or shorter or shallower. The isolation gap serves to facilitate shaping of materials formed in and around the isolation gap, which formation can be by one or more additive processes, or by one or more subtractive processes, or both. The aforementioned shaped materials serve as an isolation barrier. Further details are presented infra.

It is to be appreciated that the radiation sources illustrated in FIG. 1B can output light in a variety of wavelengths (e.g., colors) according to various embodiments of the present disclosure. Depending on the application, color balance can be achieved by modifying color generated by LED devices using a wavelength-modifying material (e.g., a phosphor material). In one embodiment, the phosphor material may be mixed with encapsulating material (e.g., silicone material) that distributes phosphor color pixels within a thin layer atop the array of LED devices. Other embodiments for providing color pixels can be conveniently constructed using a cover member (see FIG. 1C) that comprises deposits of one or more wavelength-modifying materials.

FIG. 1C is a simplified diagram illustrating an optical device 150 embodied as a light source 142 constructed using an array of LEDs juxtaposed with a cover member 140, the cover member having a mixture of wavelength converting materials distributed within the volume of the cover member, according to some embodiments. The wavelength converting materials can be distributed in a variety of configurations. For example, the light source 142 can include blue color emitting material at its corners, green color emitting material at its edges, and red color emitting material at its center. Individually, and together, these color pixels modify the color of light emitted by the LED devices. For example, the color pixels are used to modify the light from LED devices to appear as white light having a uniform broadband emission (e.g., characterized by a substantially flat emission of light throughout the range of about 380 nm to about 780 nm), which is suitable for general lighting. In one embodiment, “blank” pixels are used for later color tuning and the color of the light from LED devices is measured.

In various embodiments, color balance adjustment is accomplished by using pure color pixels, mixing phosphor material, and/or using a uniform layer of phosphor over LED devices. In one embodiment, color balance tuning is achieved by providing a color pattern on a cover member 140. Or, the cover member can be is made of glass material and function as a 405 nm reflection dichroic lens. Hermetic sealing techniques may be used to encapsulate the cover member within the optical device 150. A color tuning using cover member can also be achieved through light absorption and/or light reflection.

In one embodiment, a predeposited phosphor plate is attached to the cover member based on a predetermined pattern. For example, after positioning wavelength-modifying material in the vicinity of the light emitting devices, the color of the aggregate emitted light by the optical device 150 is measured. Based on the measured color, the positioning of the wavelength-modifying material is determined and used to balance the color of the aggregate emitted light. Various wavelength converting processes are discussed infra.

In an alternative embodiment, wavelength converting processes are facilitated by using one or more pixilated phosphor plates that are attached to the cover member. For example, the pixilated phosphor plates include color and, depending on the application, color patterns of the phosphor plate may be predetermined based on the measured color balance of the aggregate emitted light. In an alternative embodiment, the absorption plate, which is attached to the cover member, is used to perform color correction. In some situations, the absorption plate comprises color absorption material. For example, the absorbing and/or reflective material can be plastic, ink, die, glue, epoxy, and others.

In other embodiments, the phosphor particles are embedded in a reflective matrix (e.g., the matrix formed by conductive contacts). Such phosphor particles can be disposed on the substrate by deposition. In one specific embodiment, the reflective matrix comprises silver or other suitable material. Alternatively, one or more colored pixilated reflector plates (not shown) are attached to the cover member to adjust color balance of the LED devices. In some situations, materials such as aluminum, gold, platinum, chromium, and/or others are deposited on the pixilated reflector plates to provide color balance.

FIG. 1D is a simplified diagram illustrating an LED lamp 160 having a base to provide a mount point for a light source, according to some embodiments. It is to be appreciated that an LED lamp 160, according to the present disclosure, can be implemented for various types of applications. As shown in FIG. 1D, a light source (e.g., the light source 142) is a part of the LED lamp 160. The LED lamp 160 includes a base member 151. The base member 151 is mechanically connected to a heat sink 152. In one embodiment, the base member 151 is compatible with conventional light bulb socket and is used to provide electrical power (e.g., using an AC power source) to the one or more radiation emitting devices (e.g., one or more instances of light source 142).

FIG. 2 is a simplified diagram illustrating a chip-array-based apparatus 200 having green and red wavelength converting material. Compared to the device shown in FIG. 1A, only two layers of wavelength converting materials are used. This example shows a transparent (non-converting layer) as well as a layer of green wavelength converting materials 202 and a layer of red wavelength converting materials 204. The LED devices (e.g., LED device 201) comprising the array are blue-emitting. The combination of blue LED light emission and the green and red wavelength converting materials emission results in white light.

FIG. 3A is a simplified diagram illustrating a conversion process 300. As shown, a radiation source 301 is configured to emit radiation at violet, near ultraviolet, or UV wavelengths. The radiation emitted by radiation source 301 is absorbed by the phosphor materials (e.g., the blue phosphor material 302, the green phosphor material 303, and the red phosphor material 304). Upon absorbing the radiation, the blue phosphor material 302 emits blue light, the green phosphor material 303 emits green light, and the red phosphor material 304 emits red light. As shown, a portion (e.g., portion 310 ₁, portion 310 ₂) of the emissions from the blue phosphor are incident on the surrounding phosphors, and are absorbed by the green phosphor material and red phosphor material, which emits green and red light, respectively. This particular process of converted blue light being further absorbed and converted (e.g., in a cascade of emission and absorption) is considered a lossy process, and in some cases can be undesirable.

FIG. 3B is a simplified diagram illustrating a conversion process 350. As shown, a radiation source 351 is configured to emit radiation at a wavelength that is substantially in the blue spectrum. The radiation emitted by radiation source 351 is reflected by blue light emitting wavelength converting material 352 and absorbed by the green light emitting wavelength converting material 353 and red light emitting wavelength converting material 354. Upon absorbing the radiation, green light emitting wavelength converting material 353 emits green light, and the red light emitting wavelength converting material 354 emits red light. A portion of the converted blue light is absorbed by the green light emitting wavelength converting material and red light emitting wavelength converting material, which emits green and red light, respectively. This particular process of converted blue light being further absorbed and converted is considered a lossy process, and in some cases can be undesirable.

FIG. 4 is a graph illustrating a light process chart 400 by phosphor material. As shown in FIG. 4, radiation with a wavelength of violet, near violet, or ultraviolet from a radiation source is absorbed by the blue phosphor material, which in turn emits blue light. However, since the blue color light can also be absorbed by red and green phosphor, a portion of the blue light is converted to green or red light. As shown in FIG. 4, each phosphor is most effective at converting radiation at its particular range of wavelength. And, as shown, some of these ranges overlap. In particular, the wavelength range from about 380 nm to about 430 nm (shown as wavelength range 411) exhibits absorption by all three phosphors (e.g., blue, green, and red). However, the wavelength range from about 430 nm to about 500 nm (shown as wavelength range 419) exhibits absorption by substantially only two phosphors (e.g., green, and red). Thus, the effect of the lossy conversion processes (e.g., conversion process 300 and conversion process 350) in absorbing blue light from the radiation sources, and re-absorbing blue-emitted light from the wavelength converting materials, is reduced.

Yet, it remains a challenge with UV- or V-pumped embodiments (e.g., pcLEDs) where there remains a requirement for a short pump wavelength to excite a blue phosphor while reducing the lossy effects as heretofore described. Among other challenges, the short wavelength light is susceptible to optical loss in materials typically employed in the fabrication of LEDs including GaN semiconductor material, packaging material, contacts and metallization (especially Ag) material, and encapsulation material (e.g., silicone or epoxy). Furthermore, short wavelength LEDs that pump a blue phosphor may generate blue photons which subsequently pump lower-energy phosphors (e.g., green and red), as illustrated in FIG. 4. This cascading event is lossy, according to the quantum efficiency of the blue phosphor, thereby reducing color conversion efficiency. It is thus desirable to maintain the benefits of UV- and/or V-based LEDs while maintaining high conversion efficiency.

It is to be appreciated that embodiments of the present disclosure maintain the benefits of UV- and/or V-pumped pcLEDs while improving conversion efficiency. In one embodiment, an array of LED chips is provided, and is comprised of two groups. One group of LEDs has a shorter wavelength to enable pumping of a blue phosphor material. The second group of LEDs has a longer wavelength which may, or may not, excite a blue phosphor material, but will excite a green or longer wavelength (e.g., red) phosphor material. For example, the first group of LEDs might have an average emission wavelength of less than 405 nm, while the second group may have an average emission wavelength greater than 405 nm. The combined effect of the two groups of LEDs in the array is to provide light of desired characteristics such as color (e.g., white) and color rendering. Furthermore, the conversion efficiency achieved in the preferred embodiment will be higher than that of the conventional approach. In particular, the cascading loss of blue photons pumping longer-wavelength phosphors may be reduced by localizing blue phosphor to regions near the short-wavelength LEDs. In addition, the longer-wavelength pump LEDs will contribute to overall higher efficacy by being less susceptible to optical loss mechanisms in GaN, metallization, and packaging materials, as described above.

FIG. 5 is a simplified diagram illustrating an optical device, according to an embodiment of the present disclosure. As shown in FIG. 5, an optical device 500 includes a submount 111 (not shown) that has a surface. A number of radiation sources are provided on the submount. According to various embodiments, two types of radiation sources are provided, and each type of radiation source is associated with a range of wavelength. For example, radiation sources include a first plurality of radiation sources that are configure to emit radiation characterized by a first wavelength. More specifically, the first wavelength can have a range of between about 380 nm to 470 nm. In a specific embodiment, the first wavelength is characterized by a peak emission of about 420 nm to 470 nm. The first plurality of radiation sources is positioned on the surface, and the first plurality of radiation sources comprising n number of radiation sources. For example, the first plurality of radiation sources includes “long” violet LED devices 501 and 506.

The radiation sources also include a second plurality of radiation sources that are configured to emit radiation characterized by a second wavelength. In exemplary embodiments, the second wavelength is shorter than the first wavelength. More specifically, the second wavelength is violet or ultraviolet. In a specific embodiment, the second plurality of radiation sources is characterized by a peak emission in the range of about 380 nm to about 430 nm. In a certain embodiment, the second wavelength is less than 390 nm. The second plurality of radiation sources is positioned on the surface of the submount. The second plurality of radiation sources includes m number of radiation sources. The ratio between the number m and the number n is predetermined based on a selected wavelength. Typically, for warm color temperatures, n is greater than m. The ratio of n to m can be 1:1, 2:1, 10:1, and other ratios. For example, the ratio can be based on a selected wavelength output for the optical device 500. As an example, the second plurality of radiation sources comprises LED devices 505 and 507.

Depending on the application, the arrangement of a first plurality and a second plurality of radiation sources can be based on various criteria. For example, particular patterns can be used to maximize the efficiency of the optical device 500.

The optical device 500 includes three wavelength converting layers overlaying the radiation sources: a first wavelength converting layer 503, a second wavelength converting layer 502, and a third wavelength converting layer 504. The first wavelength converting layer 503 is configured to absorb at least a portion of radiation emitted by both the first plurality of radiation sources and the second plurality of radiation sources. More specifically, the first wavelength converting layer is associated with a wavelength emission ranging from 590 nm to 650 nm. For example, the first wavelength converting layer comprises red phosphor material that is adapted to emit substantially red color light.

The second wavelength converting layer 502 is configured to absorb at least a portion of radiation emitted by the first plurality of radiation sources and the second plurality of radiation sources. The second wavelength converting layer is associated with a wavelength emission ranging from 490 nm to 590 nm. For example, the second wavelength converting layer comprises a green phosphor that is adapted to emit substantially green light.

The third wavelength converting layer 504 is configured to absorb at least a portion of radiation emitted by the second plurality of radiation sources. The third wavelength converting layer is associated with a wavelength emission ranging from 440 nm to 490 nm. For example, the third wavelength converting layer comprises a blue phosphor material that is adapted to emit substantially blue light.

Depending on the application, the optical device 500 may include other components as well. In certain embodiments, the optical device 500 includes a power source that is capable of selectively powering the radiation sources or LED devices. In a specific embodiment, the power source is configured to turn radiation sources on and off based on the desired color output. For example, by selectively turning off the radiation source of a specific wavelength, the color output of the optical device is changed. More particularly, a driving circuit can be configured to selectively power the first plurality of radiation devices while maintaining a constant power to the second plurality of radiation sources. Or, the driving circuit can be configured to tune to a ratio of energy being delivered to the first plurality of radiation sources as compared to energy delivered to the second plurality of radiation sources.

In certain embodiments, the power source is configured to turn off certain radiation sources for dimming purposes. The optical device 500 can also include other components such as a housing member, sealing material, transparent cover, encapsulating material, and others. And, in certain embodiments, patterned phosphor materials are used.

FIG. 6 is a simplified diagram illustrating an optical device 600, according to an embodiment of the present disclosure. As shown in FIG. 6, an optical device 600 includes a submount 111 (not shown) that has a surface. A number of radiation sources are provided on the submount. According to various embodiments, two types of radiation sources are provided, and each type of radiation source is associated with a range of wavelength. For example, radiation sources include a first plurality of radiation sources that are configured to emit radiation characterized by a first wavelength. More specifically, the first wavelength can have a range of between about 380 nm to 470 nm. In a specific embodiment, the first wavelength is characterized by a peak emission at about 420 nm to 470 nm. The first plurality of radiation sources are positioned on the surface. The first plurality of radiation sources have an n number of radiation sources. For example, the first plurality of radiation sources includes LED devices 604 and 605.

The radiation sources of optical device 600 also include a second plurality of radiation sources that are configured to emit radiation characterized by a second wavelength. In various embodiments, the second wavelength is shorter than the first wavelength. More specifically, the second wavelength is violet or ultraviolet. In a specific embodiment, the second plurality of radiation sources are characterized by a peak emission in the range of about 380 nm to about 430 nm. In certain embodiments, the second wavelength is less than 390 nm. The second plurality of radiation sources is positioned on the surface of the submount. The second plurality of radiation sources comprises m number of radiation sources. The ratio between m and n is predetermined based on a selected wavelength. Typically, n is greater than m. The ratio of n to m can be 1:1, 2:1, 10:1, and other ratios. For example, the ratio is based on a selected wavelength output for the optical device 500. As an example, the second plurality of radiation sources comprises short violet LED devices 603 and 606.

In various embodiments, the arrangement of the radiation sources is patterned. More specifically, the locations of the second plurality of radiation sources are predetermined and are covered and/or surrounded by a specific phosphor pattern (e.g., phosphor pattern 607 ₁, phosphor pattern 607 ₁) . The phosphor pattern is configured to be proximal to instances from among the second plurality of radiation sources. More specifically, the phosphor pattern is more remote from the first plurality of radiation sources. The phosphor pattern is configured to absorb at least a portion of radiation emitted by the second plurality of radiation sources. In various embodiments, the phosphor pattern is associated with a wavelength emission ranging from about 440 nm to about 490 nm. In a specific embodiment, the phosphor pattern comprises blue phosphor material. For example, the patterned blue phosphor material is used to convert violet or ultraviolet radiation to blue light. Among other things, the blue light converted by the patterned phosphor material can help create desired color balance and improve efficiency.

As shown, the optical device 600 also includes a first wavelength converting layer 601 configured to absorb at least a portion of radiation emitted by the first plurality of radiation sources and the second plurality of radiation sources. The first wavelength converting layer is associated with a wavelength emission ranging from 590 nm to 650 nm. For example, the first wavelength converting layer comprises red phosphor material that is adapted to emit substantially red color light.

The second wavelength converting layers 601 and 602 are configured to absorb at least a portion of radiation emitted by the first plurality of radiation sources and the second plurality of radiation sources. The second wavelength converting layer is associated with a wavelength emission ranging from 490 mn to 590 nm. For example, the second wavelength converting layer comprises a green phosphor that is adapted to emit substantially green light.

As an example, the first and second wavelength converting layer can absorb radiation from both the first plurality and second plurality of radiation sources. Additionally, the first and second wavelength converting layers may also absorb emission from the phosphor pattern. It is to be appreciated that the embodiments of the present disclosure can provide efficiency gains over conventional techniques.

FIG. 7 is a simplified graph 700 illustrating performance of various embodiments of the optical devices described herein.

It is to be appreciated that the improvement in efficiency can be dramatic. The data shown in FIG. 7 indicates a +20% gain in conversion efficiency by pumping a tri-color phosphor mix with 405 nm radiating LEDs vs. 395 nm LEDs. In this comparison, the blue phosphor material is likely to be equally excited by both 395 nm and 405 nm LEDs, meaning the cascading loss of blue photons pumping green and/or red phosphors is still present. So, even higher gains are expected in cases for which a second group of LEDs is of a sufficiently long wavelength to not substantially pump the blue phosphor material.

FIG. 8 is a simplified diagram illustrating an optical device 800 having violet and blue LEDs according to an embodiment of the present disclosure. As shown in FIG. 8, violet LEDs and blue LEDs are arranged according to a predetermined pattern. In this configuration, green emitting and red emitting wavelength converting materials are used to convert radiation emitted by violet and blue LEDs. For example, the blue LEDs as shown are configured to provide blue color light, and as a result blue phosphor material is not needed for the optical system to produce white light.

One exemplary embodiment in accordance with the depiction of FIG. 8 comprises an optical device 800 comprising a submount having a surface, upon which surface is disposed a first plurality of radiation sources configured to emit radiation characterized by a first wavelength, the first wavelength having a range of about 440 nm to about 500 nm (e.g., radiating blue light), the first plurality of radiation sources being positioned on the surface, and the first plurality of radiation sources having n number of radiation sources. A second plurality of radiation sources configured to emit radiation is characterized by a second wavelength, the second wavelength being shorter than the first wavelength (e.g., radiating violet light), the second plurality of radiation source being positioned on the surface, and the second plurality of radiation sources having m number of radiation sources, where a ratio between m and n is predetermined based on a selected wavelength. Further, this embodiment comprises two layers of wavelength converting material, namely a first wavelength converting layer configured to absorb at least a portion of radiation emitted by the second plurality of radiation sources, the first wavelength converting layer having a wavelength emission ranging from about 590 nm to about 650 nm (e.g., red emissions), and a second wavelength converting layer configured to absorb at least a portion of radiation emitted by the second plurality of radiation sources, the second wavelength converting layer having a wavelength emission ranging from about 490 mn to about 590 nm (e.g., green emissions).

FIG. 9 is a simplified diagram illustrating an optical device 900 having violet and patterned blue LEDs according to an embodiment of the present disclosure. As shown in FIG. 9, violet LEDs and blue LEDs are arranged according to a predetermined pattern. For example, violet LEDs are characterized by a wavelength emission ranging from about 380 nm to about 430 nm, and the blue LEDs are characterized by a wavelength of about 420 nm to 490 nm. In this configuration, green phosphor materials 902 and red phosphor materials 901 are used to convert radiation emitted by violet and blue LEDs. Moreover, the blue LEDs as shown are configured to provide blue color light, and as a result blue phosphor material is not needed for the optical system to produce white light. For example, the blue LEDs are provided at predetermined locations (e.g., predetermined location 910 ₁, predetermined location 910 ₂, and predetermined location 910 ₃) that are substantially remote from green and red phosphor material, which allows the blue LEDs to efficiently emit blue colored light that contributes to white light output. In some embodiments, the blue LEDs are provided at predetermined locations that are substantially surrounded by isolation barriers (e.g., isolation barrier 911 ₁, isolation barrier 911 ₂) such that the blue LEDs emit blue colored light that does not substantially interact with the green- and red-emitting wavelength converting materials.

FIG. 10 is a simplified diagram illustrating an optical device 1000 having violet and red LEDs according to an embodiment of the present disclosure. As shown in FIG. 10, violet LEDs and red LEDs are arranged according to a predetermined pattern. For example, violet LEDs are characterized by a wavelength emission ranging from about 380 nm to about 430 nm, and the red LEDs are characterized by a wavelength of about 590 nm to 650 nm. In this configuration, green and blue phosphor materials are used to convert radiation emitted by violet and red LEDs. For example, the red LEDs as shown are configured to provide red color light, and as a result red phosphor material is not needed for the optical system to produce white light. For example, red light combines with blue and green light from blue and green phosphor material to form white light.

FIG. 11 is a simplified diagram illustrating an optical device 1100 having violet and red LEDs according to an embodiment of the present disclosure. As shown in FIG. 11, violet LEDs and red LEDs are arranged according to a predetermined pattern. For example, violet LEDs are characterized by a wavelength emission ranging from 380 nm to 430 nm, and the red LEDs are characterized by a wavelength of about 590 nm to 650 nm. In this configuration, green and blue phosphor materials are used to convert radiation emitted by violet and red LEDs. For example, the red LEDs as shown are configured to provide red color light, and as a result red phosphor material is not needed for the optical system to produce white light. In this example, red light combines with blue and green light from blue and green phosphor material to form white light.

In yet another embodiment, violet LEDs and red LEDs are arranged according to a predetermined pattern. For example, violet LEDs are characterized by a wavelength emission ranging from 380 nm to 430 nm, and the red LEDs are characterized by a wavelength of about 590 nm to 650 nm. In this configuration, green and blue wavelength-emitting materials are used to convert radiation emitted by violet LEDs. For example, the red LEDs as shown are configured to provide red color light, and as a result red wavelength- emitting material is not needed for the optical system to produce white light. For example, red light combines with blue and green light from blue and green wavelength- emitting material to form white light.

FIG. 12A is a simplified diagram 1200 illustrating an optical device having red, green, and blue radiation sources disposed within recesses. In embodiments wherein portions of the final white light spectrum are contributed by direct emission from radiation sources, it is desirable to avoid interaction of such direct emission with any wavelength converting materials (e.g., down-conversion materials, phosphors). For example, for blue-emitting radiation sources whose spectra are being combined with other radiation sources that are pumping to longer wavelength down-conversion media (e.g., to make broader spectrum light), the down-conversion media can be isolated from the optical path of the blue-emitting LEDs. And, providing such an isolation (e.g., using an isolation barrier) increases efficiency as there are losses (e.g., backscattered light into LED chip) associated with down-conversion. Instead, it is preferable to provide optical means (e.g., an isolation barrier) to reflect light from the radiation sources towards the desired optical far-field such that this reflected light does not substantially interact with down-conversion media.

One such an embodiment is shown in FIG. 12A. As shown, LEDs are placed into recessed regions in a submount (e.g., substrate or package) such that they are optically isolated from one another. Further, light from direct-emitting LEDs does not interact with down-conversion media and instead, is substantially directed into the desired emission pattern of the entire LED package. Conversely, light from the down-converted LEDs (e.g., down-converting LED 1204 ₁, down-converting LED 1204 ₂) is converted locally and directed to the final emission pattern. In addition to providing efficient light collection from the direct-emitting LEDs, this design avoids cascading down-conversion events (e.g., violet down-converted to green, and green down-converted to red) which can unnecessarily reduce overall efficiency since quantum yields of down-conversion media are less than 100%.

Light from the individual LEDs are combined together in the far field to provide a uniform broadband emission which is a combination of light from the direct-emitting and down-converting LED chips.

FIG. 12B is a simplified diagram illustrating an optical device having red, green, and blue LEDs disposed between barriers. In the embodiment of FIG. 12B, the same benefits pertaining to disposition of radiation sources in proximity to isolation barriers are provided by fabrication of the isolation barriers using an additive, rather than subtractive process. In an additive processes, the barrier is formed by techniques such as overmolding, deposition/lithography/removal, attachment of a barrier mesh, etc. In subtractive processes, the recesses are formed by techniques such as deposition/lithography/removal and other techniques well known in the art.

The radiation sources can be implemented using various types of devices, such as light emitting diode devices or laser diode devices. In certain embodiments, the LED devices are fabricated from gallium and nitrogen submounts, such as GaN submount. As used herein, the term GaN submount is associated with Group III-nitride based materials including GaN, InGaN, AlGaN, or other Group III containing alloys or compositions that are used as starting materials. Such starting materials include polar GaN submounts (e.g., submount 111 where the largest area surface is nominally an (h k l) plane wherein h=k=0, and l is non-zero), non-polar GaN submounts (e.g., submount material where the largest area surface is oriented at an angle ranging from about 80-100 degrees from the polar orientation described above towards an (h k l) plane wherein l=0, and at least one of h and k is non-zero), or semi-polar GaN submounts (e.g., submount material where the largest area surface is oriented at an angle ranging from about +0.1 to 80 degrees or 110-179.9 degrees from the polar orientation described above towards an (h k l) plane wherein l=0, and at least one of h and k is non-zero).

The wavelength converting layers mentioned above are wavelength conversion materials, which can be ceramic or semiconductor particle phosphors, ceramic or semiconductor plate phosphors, organic or inorganic downconverters, upconverters (anti-stokes), nanoparticles, and other materials which provide wavelength conversion. Some examples are listed below:

(Sr,Ca)10(PO4)6*B2O3:Eu2+ (wherein 0<n^1)

(Ba,Sr,Ca)5(PO4)3(Cl,F,Br,OH):Eu2+,Mn2+

(Ba,Sr,Ca)BPO5: Eu2+,Mn2+

Sr2Si3O8*2SrCl2:Eu2+

(Ca,Sr,Ba)3MgSi2O8:Eu2+, Mn2+

BaAl8O13:Eu2+

2SrO*0.84P2O5*0.16B2O3:Eu2+

(Ba,Sr,Ca)MgAl10O17:Eu2+,Mn2+

K2SiF6:Mn4+

(Ba,Sr,Ca)Al2O4:Eu2+

(Y,Gd,Lu,Sc,La)BO3:Ce3+,Tb3+

(Ba,Sr,Ca)2(Mg,Zn)Si2O7:Eu2+

(Mg,Ca,Sr,Ba,Zn)2Si1_xO4_(—)2x:Eu2+(wherein 0<x=0.2)

(Sr,Ca,Ba)(Al,Ga,m)2S4:Eu2+

(Lu,Sc,Y,Tb)2_u_vCevCa1+uLiwMg2_wPw(Si,Ge)3_w012_u/2 where −O.SSu^l;

0<v£Q.1; and OSw^0.2

(Ca,Sr)8(Mg,Zn)(SiO4)4Cl2:Eu2+,Mn2+

Na2Gd2B2O7:Ce3+,Tb3+

(Sr,Ca,Ba,Mg,Zn)2P2O7:Eu2+,Mn2+

(Gd,Y,Lu,La)2O3:Eu3+,Bi3+

(Gd,Y,Lu,La)2O2S:Eu3+,Bi3+

(Gd,Y,Lu,La)VO4:Eu3+,Bi3+

(Ca,Sr)S:Eu2+,Ce3+

(Y,Gd,Tb,La,Sm,Pr,Lu)3(Sc,Al,Ga)5_nO12_(—)3/2n:Ce3+ (wherein 0^0^0.5)

ZnS:Cu+,Cl˜

ZnS:Cu+,Al3+

ZnS:Ag+,Al3+

SrY2S4:Eu2+

CaLa2S4:Ce3+

(Ba,Sr,Ca)MgP2O7:Eu2+,Mn2+

(Y,Lu)2WO6:Eu3+,Mo6+

CaWO4

(Y,Gd,La)2O2S:Eu3+

(Y,Gd,La)2O3:Eu3+

(Ca,Mg)xSyO:Ce

(Ba,Sr,Ca)nSinNn:Eu2+ (wherein 2n+4=3n)

Ca3(SiO4)Cl2:Eu2+

ZnS:Ag+,Cl˜

(Y,Lu,Gd)2_nCanSi4N6+nCl_n:Ce3+, (wherein OSn^O.5)

(Lu,Ca,Li,Mg,Y)alpha-SiA;ON doped with Eu2+ and/or Ce3+

(Ca,Sr,Ba)SiO2N2:Eu2+,Ce3+

(Sr,Ca)AlSiN3:Eu2+

CaAlSi(ON)3:Eu2+

Sr10(PO4)6C12:Eu2+

(BaSi)O12N2:Eu2+

SrSi2(O,Cl)2N2:Eu2+

(Ba,Sr)Si2(O,Cl)2N2:Eu2+

LiM2O8:Eu3+ where M=(W or Mo)

For purposes of the application, it is understood that when a phosphor has two or more dopant ions (e.g., those ions following the colon in the above phosphors), this is to mean that the phosphor has at least one (but not necessarily all) of those dopant ions within the material. That is, as understood by those skilled in the art, this type of notation means that the phosphor can include any or all of those specified ions as dopants in the formulation. It is to be understood that nanoparticles, quantum dots, semiconductor particles, and other types of materials can be used as wavelength converting layers for color conversion as well.

FIG. 13 is an exploded view of an LED lamp, according to some embodiments. The exploded view illustrates an LED lamp 1300 with an MR-16 type design. As shown, a finned heat sink 1302 is provided and one or more optical devices 150 (e.g., light source 142) can be positioned on the surface. Also shown in the exploded view is a cover member 140, the cover member having a mixture of wavelength converting materials distributed within the volume of the cover member. An LED lamp 1300 can comprise an insertable reflector 1304, and a protective lens 1301.

For embodiments powered by an external power source (e.g., a power source from outside the lamp), a housing 1306 is provided. As shown, the housing 1306 is configured to provide an electrical connection to an external power source. Further, such a housing comprises an interior void, suitable for containing electrical components (e.g., a driver), possibly disposed on a printed circuit board.

FIG. 14 is an illustration of an LED system 1400 comprising an LED lamp 1410, according to some embodiments. The LED system 1400 is powered by an AC power source 1402, to provide power to a rectifier module 1416 (e.g., a bridge rectifier) which in turn is configured to provide a rectified output to an array of radiation emitting devices (e.g., a first array of radiation emitting devices, a second array of radiation emitting devices) comprising a light source 142. A current monitor module 1405 is electrically coupled to the first array and second array of radiation emitting devices such that the current monitor module can determine a first current level associated with the first array of radiation emitting devices and a second current level associated with the second array of radiation emitting devices; and a signal compensating module 1414 electrically coupled to the current monitor module 1405, the signal compensating module being configured to generate a first compensation factor signal based on a difference between the first current level and a first reference current level. As shown, the rectifier module 1416 and the signal compensating module (and other components) are mounted to a printed circuit board 1403. Further, and as shown, the printed circuit board 1403 is electrically connected to a power pin 1415 mounted within a base member 151, and the base is mechanically coupled to a heat sink 152. The heat sink and base provide mechanical stability for an insertable reflector 1304.

FIG. 15 depicts a block diagram of a system to perform certain functions to fabricate an optical device. As an option, the present system 1500 may be implemented in the context of the architecture and functionality of the embodiments described herein. Of course, however, the system 1500 or any operation therein may be carried out in any desired environment. The operations of the system can, individually or in combination, perform method steps within system 1500. Any method steps performed within system 1500 may be performed in any order unless as may be specified in the claims. As shown, FIG. 15 implements fabrication of an optical device, comprising one or more steps for: preparing a submount having a surface (see module 1510); disposing a first plurality of radiation sources configured to emit radiation characterized by a first wavelength, the first wavelength having a range of about 440 nm to about 500 nm, the first plurality of radiation sources being positioned on the surface, the first plurality of radiation sources having n number of radiation sources (see module 1520); disposing a second plurality of radiation sources configured to emit radiation characterized by a second wavelength, the second wavelength being shorter than the first wavelength, the second plurality of radiation source being positioned on the surface, the second plurality of radiation sources having m number of radiation sources, where a ratio between m and n being predetermined based on a selected wavelength (see module 1530); providing a first wavelength converting layer configured to absorb at least a portion of radiation emitted by the second plurality of radiation sources, the first wavelength converting layer having a wavelength emission ranging from about 590 nm to about 650 nm (see module 1540); providing a second wavelength converting layer configured to absorb at least a portion of radiation emitted by the second plurality of radiation sources, the second wavelength converting layer having a wavelength emission ranging from about 490 mn to about 590 nm (see module 1550).

In one or more preferred embodiments, various pattern and/or arrangement for different radiation sources can be used. The above description and illustrations should not be taken as limiting the scope of the present disclosure which is defined by the appended claims. 

What is claimed is:
 1. An optical device comprising: a mounting surface; at least one first light emitting diode source, the at least one first light emitting diode source emitting radiation characterized by a first wavelength within a range from about 430 nm to about 480 nm, wherein the at least one first light emitting diode source is configured on the mounting surface; at least one second light emitting diode source emitting radiation characterized by a second wavelength, the second wavelength being shorter than the first wavelength, wherein the at least one second light emitting diode source is configured on the mounting surface; and a first wavelength-converting material positioned in an optical path of radiation from the at least one first light emitting diode source and configured to convert radiation from the first wavelength to radiation at a wavelength within a range from about 500 nm to about 600 nm; wherein the optical device outputs a resulting radiation from at least the first light emitting diode source, the at least one second light emitting diode source, and the first wavelength-converting material.
 2. An optical device comprising: a mounting surface; a plurality of first light emitting diode sources, each of the plurality of first light emitting diode sources emitting radiation characterized by a first wavelength within a range from about 430 nm to about 480 nm, wherein the plurality of first light emitting diode sources is configured on the mounting surface; at least one second light emitting diode source emitting radiation characterized by a second wavelength, the second wavelength being shorter than the first wavelength, wherein the at least one second light emitting diode source is configured on the mounting surface; a first wavelength-converting material positioned in an optical path of radiation from at least one of the plurality of first light emitting diode sources and configured to convert radiation from the first wavelength to radiation at a wavelength within a range from about 500 nm to about 600 nm; and a second wavelength-converting material positioned in an optical path of radiation from at least one of the plurality of first light emitting diode sources and configured to convert radiation from the first wavelength to radiation at a wavelength within a range from about 590 nm to about 650 nm; wherein the optical device outputs a resulting radiation from at least the plurality of first light emitting diode sources, the at least one second light emitting diode source, the first wavelength-converting material, and the second wavelength-converting material.
 3. An optical device comprising: a mounting surface; a plurality of first light emitting diode sources, each of the plurality of first light emitting diode sources emitting radiation characterized by a first wavelength within a range from about 430 nm to about 480 nm, wherein the plurality of first light emitting diode sources is configured on the mounting surface; at least one second light emitting diode source emitting radiation characterized by a second wavelength, the second wavelength being shorter than the first wavelength, wherein the at least one second light emitting diode source is configured on the mounting surface; and a first wavelength-converting material positioned in an optical path of radiation from at least one of the plurality of first light emitting diode sources and configured to convert radiation from the first wavelength to radiation at a wavelength within a range from about 500 nm to about 600 nm; wherein the plurality of first light emitting diode sources and the at least one second light emitting diode source are configured spatially on the mounting surface and are characterized by a predetermined ratio represented by a first number of first light emitting diode sources to a second number of second light emitting diode sources; and wherein the optical device outputs a resulting radiation from at least the first plurality of light emitting diode sources, the at least one second light emitting diode source, and the first wavelength-converting material.
 4. The optical device of claim 3, wherein the second wavelength is within a range from about 380 nm to about 430 nm.
 5. The optical device of claim 3, wherein the first wavelength-converting material is positioned in the optical path of radiation from at least one of the at least one second light emitting diode sources and is configured to convert radiation from the first wavelength and from the second wavelength.
 6. The optical device of claim 3, comprising a second wavelength-converting material positioned in an optical path of radiation from at least one of the plurality of first light emitting diode sources and configured to convert radiation from the first wavelength to radiation at a wavelength within a range from about 590 nm to about 650 nm.
 7. The optical device of claim 3, comprising a second wavelength-converting material positioned in an optical path of radiation from the at least one of the at least one second light emitting diode source and configured to convert radiation from the second wavelength to radiation at a wavelength within a range from about 590 nm to about 650 nm.
 8. The optical device of claim 3, comprising a second wavelength-converting material positioned in an optical path of radiation from at least one of the plurality of first light emitting diode sources and from at least one of the at least one second light emitting diode source, and configured to convert radiation from the first wavelength and from the second wavelength to radiation at a wavelength within a range from about 590 nm to about 650 nm.
 9. The optical device of claim 8, where the first wavelength-converting material and the second wavelength-converting material are mixed with encapsulating material.
 10. The optical device of claim 3, comprising at least one third light emitting diode source emitting radiation characterized by a third wavelength, the third wavelength being longer than the first wavelength, wherein the at least one third light emitting diode source is configured on the mounting surface.
 11. The optical device of claim 10, wherein the third wavelength is within a range from about 590 nm to about 650 nm.
 12. The optical device of claim 3, wherein, the plurality of first light emitting diode sources comprises n first light emitting diodes; the at least one second light emitting diode source comprises m second light emitting diodes; and a ratio of the number n to the number m (n:m) is greater than
 1. 13. The optical device of claim 3, wherein the optical device is configured to emit substantially white light.
 14. The optical device of claim 3, wherein the plurality of first light emitting diode sources and the at least one second light emitting diode source comprise a gallium- and nitrogen-containing material.
 15. The optical device of claim 3, wherein the plurality of first light emitting diode sources and the at least one second light emitting diode source are configured in an array pattern.
 16. The optical device of claim 3, wherein the mounting surface comprises a single mounting surface.
 17. The optical device of claim 3, further comprising an optical system.
 18. The optical device of claim 3, where the first wavelength-converting material is remote from the plurality of first light emitting diode sources.
 19. The optical device of claim 3, wherein the resulting radiation is emanated through a light emitting surface, the light emitting surface having a predetermined shape selected from a square, a rectangle, a hexagon, a regular polygon, and a circle.
 20. The optical device of claim 3, where the plurality of first light emitting diode sources and the at least one second light emitting diode source are connected to a common electrical circuit enabling electrical injection. 